This invention relates generally to a fastening system for a locking nut threadform in which a wrench socket applies a visual mark when a preset torque is reached.
Aerospace, automotive and biomechanical technologies are evolving such that engineers in these fields are pursuing more reliable, lower cost and lighter weight assembly techniques. Traditionally, the weak point in the design and manufacture of structural parts has often been the attachment system. Many situations are known where nuts and bolts have become loosened during high vibration situations, thus leading to product failure. Nowhere has this been more prevalent than in space shuttle boosters, aircraft wingplates, automotive suspension systems and prosthetic joints.
Furthermore, the process of tightening and inspecting a large set of nuts and bolts can be an expensive, tedious and mistake filled task. Currently, a mechanic must work his way along a set of nuts, serially tightening and then re-tightening the nuts, and then an inspector will check for the proper torque on each of these fasteners. Throughout both the tightening and inspection processes nuts may be missed and other nuts may be over torqued, either of which leads to premature failure.
Nevertheless, a torque-limiting system is currently being used which visually marks nuts which have a buttress threadform. This torque-limiting nut driving system uses a wrench socket containing a ball set. When the socket is used to tighten the locking nut, the ball set engages portions of the nut head and eventually penetrates through these portions when the proper torque is reached. If re-torquing is required, then a second socket with a uniquely located ball set can be used, thereby visually marking the locking nut head in a different location. The fastening process for this system has been disclosed in U.S. Pat. No. 4,881,316 entitled "Process For Setting A Threaded Torque-Limited Collar And Pin Joint," issued to Wing on Nov. 21, 1989; and, 4,858,299 entitled "Process For Making A Joint With A Torque-Limited Collar," issued to Wing on Aug. 22, 1989, both of which are incorporated by reference herewithin. The related collar or nut with the buttress threadform has been described in U.S. Pat. No. 4,784,549 entitled "Torque-Limited Collar," issued to Wing on Nov. 15, 1988, also incorporated by reference herewithin.
Furthermore, a locking nut and bolt threadform, independent from any fastening method such as the preceding, has been described in U.S. Pat. No. 4,171,012, entitled "Locking Thread Construction", issued on Oct. 16, 1979 to Holmes, incorporated by reference herewithin. Further, a similar locking threadform has been shown for a self tapping screw in U.S. Pat. No. 4,258,607, entitled "Vibration Resistant Screw", issued on Mar. 31, 1981 to McKewan, also incorporated by reference herewithin. Although both of these patents relate to a locking threadform, neither suggests using a torquing device that visually marks the locking nut.